I. Field
The following description relates generally to wireless communications systems and more particularly to voice call continuity.
II. Background
Wireless communication systems are widely deployed to provide various types of communication and to communicate information regardless of where a user is located (e.g., inside or outside a structure) and whether a user is stationary or moving (e.g., in a vehicle, walking). For example, voice, data, video and so forth can be provided through wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources. A system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless communication networks are established through a mobile device communicating with a base station or access point. The access point covers a geographic range or cell and, as the mobile device is operated, the mobile device can be moved in and out of these geographic cells.
Traditional wireless communication networks are circuit switch networks. In circuit switch networks, when a data transfer (e.g., voice call or other type of communication) is initiated, the data transfer is routed to a cellular infrastructure, such as a Base Station Controller (BSC) or mobile switching center (MSC). After routing to the cellular infrastructure, the data transfer is routed to the recipient, which can be another cellular network, a public switch telephone network, and so on.
Recently, Voice over Internet Protocol (VoIP) technology has been advancing and IP-Multimedia Subsystem (IMS) technology has been developed. Some networks are actively deploying VoIP and/or IMS technology. This has resulted in at least two networks: the legacy circuit switch network and the new VoIP/IMS network. Since the VoIP/IMS network is deployed from the ground up (e.g., an entirely new infrastructure is built), for some time the coverage provided by the VoIP/IMS network will be limited and/or there will be pockets of such coverage at various locations.
Further, in a Voice Call Continuity (VCC) architecture, all calls originated by VCC subscribers are anchored at the VCC Application Server (AS). In some networks, operators may choose to disable anchoring of calls (Selective Anchoring). Operators may also choose to disable anchoring of calls for roaming subscribers. The calls originated in the Circuit Switch (CS) domain are anchored using Customized Applications for Mobile Network Enhanced Logic (CAMEL) triggers and/or Wireless Intelligent Network (WIN) triggers by the Mobile Switching Center (MSC). On the other hand, calls originated in the IP-Multimedia Subsystem (IMS) domain are anchored utilizing an initial Filter Criteria (iFC) at the Serving-Call Session Control Function (S-CSCF).
Due to the limited and/or non-contiguous nature of IMS networks, when a mobile device attempts to transfer a communication (e.g. voice call, data communication, and so forth) between a circuit switch network and an IMS network (or from the IMS network to the circuit switch network), there is a potential for a communication failure. For example, the call can dropped when crossing the network boundaries and/or when the call is handed off between the two networks.